Use is made of aqueous solutions of quaternary salts (I) to prepare polymers intended to act as flocculants in water treatment.
The main problems which are posed during the synthesis of the quaternary salts (I) are, on the one hand, the sensitivity to water of the monomers (II) and, on the other hand, the risks of polymerization of the reaction mixture in the reactor and those of the quaternary salts (I) on storage.
Japanese Patent Applications JP-A-57 109 747 and JP-A-57 109 749 describe a process for stabilizing salts of formula (I). This process consists in adding, to these salts, at least one chelating agent which can be an aminocarboxylic acid and respectively a nitrose compound or a compound of quinone type. In practice, ethylenediaminetetraacetic acid (EDTA) and the trisodium salt of nitrilotriacetic acid have been experimented with as aminocarboxylic acid, either with a nitroso compound or with benzoquinone, in order to stabilize an aqueous methacryloyloxyethyltrimethylammonium chloride solution.
EDTA is also the only sequestering agent cited in European Patent Application EP-A-302 122, which describes a process for the preparation of unsaturated quaternary ammonium salts by quaternization in a medium composed of water and an aprotic organic solvent.